This invention relates generally to improvements in irrigation sprinklers of the type having a rotatable spray head driven by hydraulic reaction forces for sweeping an outwardly projected stream of water over a surrounding terrain area to irrigate adjacent vegetation. More specifically, this invention relates to an improved rotating stream sprinkler having a balanced drive torque and friction brake torque for maintaining a relatively slow and substantially constant spray head rotational speed over a range of normal water supply operating pressures.
Rotating stream sprinklers of the reaction drive type are known in the art for use in sweeping an outwardly projected stream of irrigation water over surrounding terrain for landscape irrigation. In one common form, a spray head is rotatably mounted on a sprinkler body and includes a nozzle port having a selected open flow area and inclination angle for outward discharge of the irrigation water stream, when the sprinkler body is connected to a supply of water under pressure. The nozzle port is offset relative to an axis of spray head rotation, whereby the outwardly projected water stream produces a reaction force for continuously rotatably driving the spray head and thereby sweeping the water stream in a continuous or uninterrupted manner over the adjacent terrain. To accommodate such rotational displacement, bearing and related seal components are interposed between the rotatable spray head and the nonrotating sprinkler body.
In the past, such rotating stream sprinklers have suffered from relatively rapid and uncontrolled rotational speeds, resulting in an undesirably reduced range or radius of throw for the projected water stream. In this regard, rotational driving of the spray head at an excessive speed occurs when the hydraulic reaction drive torque significantly exceeds the counteracting brake torque attributable, for example, to frictional resistance forces provided by the bearing and related seal components.
Attempts to reduce and regulate the speed of spray head rotation by reducing the drive torque having resulted in inconsistent sprinkler operation, particularly in response to unexpectedly increased brake torque related to intrusion of dirt and grit between bearing surfaces. Indeed, such intrusion of dirt and grit into the bearing components can increase brake torque sufficiently to prevent spray head rotation when the water supply is turned on.
Conversely, efforts to reduce and control spray head rotational speed by increasing the brake torque during normal operation, as by applying a spring force to the bearing components, have also resulted in inconsistent sprinkler operation. In particular, a thrust spring has been employed for applying an axial spring force to the bearing components, with the intent to increase the friction brake torque and thereby decrease the drive/brake torque differential to slow down the speed of spray head rotation. However, during normal sprinkler operation, drive torque attributable to increasing water supply pressure has been found to increase at a rate which significantly exceeds friction brake torque attributable to the thrust spring, whereby the spray head rotation at relatively high water supply pressures may again be inconsistent and undesirably rapid.
The present invention overcomes these problems and disadvantages by providing torque balanced reaction drive wherein drive torque and brake torque are maintained in a substantially constant ratio throughout a normal operating range of low to high water supply pressures, thereby providing a relatively slow and substantially constant spray head rotational speed.